Current automatic warewash processes involve at least 2 steps. The automatic warewash process comprises a main wash in which the substrates are cleaned by pumping a main wash solution over the substrates via nozzles. The main wash solution is obtained by dissolving main wash detergent, which may contain components such as alkalinity agents, builders, bleaches, enzymes, surfactants, polymers, corrosion inhibitors etc. A further step comprises rinsing after the main wash. This rinse cycle comprises flowing warm or hot water, often containing a rinse aid, over the substrates, which may be followed by a hot air stream to further improve the drying process.
Such automatic processes take place in both domestic as well as institutional ware washing machines. There are significant differences in process parameters between these 2 type of machines, which are for instance described in international patent application WO 2006/119162. The rinse cycles in these processes vary from a few seconds (for some institutional machines) up to 40 minutes (for some domestic machines). The temperature of the rinse solution typically varies between 40 and 90° C. Despite these different parameters, both domestic and institutional processes involve a main wash and a rinse step.
The rinse solution often contains a rinse aid. Such a rinse aid typically is a liquid comprising non-ionics present in an amount of 10 to 30% in water, often in combination with hydrotropes and sometimes other additives such as acids, corrosion inhibitors, bleaches, etc. The function of the rinse aid is to provide a sheeting action of the rinse solution, which leads to improved drying of the ware and enhanced visual appearance after drying.
The presence of surfactants in current rinse aids for ware washing processes (both domestic and institutional) is considered to be essential since these surfactants reduce the surface tension of the rinse solution and so lead to improved drying properties of the substrates. The majority of these surfactants are nonionics. Hydrotopes are also important for keeping the surfactants into solution. Sometimes other components may also be present in the rinse aid; e.g. perfume, color components, acid and other scale inhibitors (to prevent scale formation on substrates and machine parts), corrosion inhibitors, soil release agents (leaving behind a thin layer leading to improved cleaning in next cleaning cycle), anti-spotting components (improving visual appearance, such as spot free drying esp. on glass).
The drying properties of rinse aids thus are primarily determined by the nonionic surfactants. Without these nonionics the substrates would not become dry or would have many spots and water marks after drying.
The presence of nonionic surfactants in current rinse aids also has several disadvantages or limitations:
Proper drying is not always obtained due to limited effectiveness. This necessitates drying with a cloth or accepting longer drying time.
Use of nonionics can have negative effects on visual appearance. Smears and streaks of residual nonionics can become visible, especially on glass.
Use of nonionics with wetting properties can lead to foam forming in the wash bath. This requires the need for a separate nonionic with defoaming properties in the rinse aid composition.
Additional of a hydrotrope is often needed to create a stable liquid rinse aid formulation.
Most nonionics are not stable or compatible in combination with acids and/or bleaches.
Most nonionics are not food approved.
Rinse aid nonionics are often difficult to disperse in the rinse solution. High mechanical forces are needed to create a homogeneous rinse solution. For this reason, rinse aids are mosttimes dosed before the boiler of institutional dishwash machines.
Residual nonionics, attached to substrates, can have negative effects on soil adhesion and for instance lead to starch build up.
WO 2004/061069 discloses a rinse aid composition comprising: a) from 0.01 to 70 wt % of at least one water-soluble metal salt; b) from 0.01 to 25 wt % of an acid; c) from 0.01 to 60 wt % of a non-ionic surfactant; d) at least a dispersant polymer and/or a perfume; and wherein said rinse aid composition has a pH of less than 5 when measured at 10% concentration in an aqueous solution. Dispersant polymers are useful in rinse aid compositions because they disperse particles in the wash solution or rinse water and so prevent particle disposition on the ware.
The present invention discloses new rinse compositions and methods that utilize polysaccharides, which can solve most of the issues and limitations of standard rinse aids. In these new compositions and methods, nonionic or other surfactants may not be required in the rinse aid for proper drying. Rather, polysaccharides present in the rinse compositions may adsorb to a washware substrate and provide for better wetting and subsequent drying of the substrate in the absence of nonionic or other surfactants, which are utilized to reduce the surface tension of the surface solution.